binations using class F and F-1 amplifiers. The opposite configuration using
a class F carrier amplifier and class F-1
peaking amplifier exhibited the worst.
This backed up the analyses and descriptions in the previous subsections.

Compared with the conventional
class AB and B based Doherty amplifier, the best configuration delivered
more output power, as much as 0.76
dB, and better PAE, as much as 6.03
percent points, at an IMD3 of - 30
dBc. Benefiting from harmonic tuning and proper selection for the carrier and peaking amplifiers, these amplifiers can further gain approximately
a 10 percent higher peak PAE for a
one-tone signal input than that of a
conventional Doherty amplifier.

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amplifiers should be carefully considered since different amplifiers are
employed as the carrier and peaking
amplifier cells.

The amplitude modulation to
phase modulation (AM to PM) characteristics for the carrier and peaking amplifiers were measured using a
network analyzer. Figure 9 shows the
measured phase responses of the carrier and peaking amplifiers. As shown,
the phase response of the peaking
amplifier experienced a huge transition due to a class B bias point while
that of the carrier amplifier appeared
to be rather flat. The phase difference
of about 54. 35° was observed around
1 dB gain compression point. It was
compensated using an input offset
line which was already presented in
Figure 8.

The Doherty amplifier based on
class F and F-1 amplifiers was implemented using the same device that
was used for the design and simulation. Figure 10 shows a photograph
of the implemented Doherty amplifier. The fundamental load impedance
of ( 21 + j19) Ω, extracted from the
class AB amplifier design, was applied
for both the class F and F-1 amplifiers. The output offset lines were also
added at the end of each amplifier,
The Doherty amplifier was evaluated
using the one-tone,
two-tone and down-link WCDMA signals. The WCDMA
signal has a PAR of
10. 5 dB at a complementary cumulative
distribution function (CCDF) of 0.01
percent. To see if
the load modulation successfully

Because conventional Doherty amplifiers are generally built with identical cells for both carrier and peaking
amplifiers, the phase difference of the
transmission coefficient between the
carrier and peaking amplifier is not
significant and can be easily compensated using a tuned input offset line.
However, in this case, the difference
in the phase response between the
class F-1 carrier and class F peaking